This invention relates to a solid-state image device, and in particular, to a solid-state image device operable at driving with low power and a high frequency.
A conventional solid-state image device of two-dimensional CCD (namely, Charge Coupled Device) type mainly includes a plurality of photo-diodes, a plurality of vertical CCD registers, a horizontal CCD register, a charge detection portion and an amplification portion.
In this event, the photo-diodes are two-dimensionally arranged on an image region, and each of them carries out a photoelectric conversion operation. Electric signal charges converted by each photo-diode are transferred to the vertical CCD register coupled to the photo-diode and are vertically sent to the horizontal CCD register.
The electric signal charges sent to the horizontal CCD register are horizontally transferred through the horizontal CCD register. The transferred signal charges are detected as a voltage by the charge detection portion and are thereafter amplified by the amplification portion.
More specifically, when an image pattern is projected on the image region of the solid-state image device by the use of an optical system, each of the photo-diodes generates electrical charges dependency on an amount of an incident light beam by the photoelectric conversion operation.
The generated electric charges are given to the vertical CCD register for a preselected period. The signal charges given to the vertical CCD register are transferred from the vertical CCD register to the horizontal CCD register for every blanking duration. Subsequently, the horizontal CCD register moves the electric charges towards the charge detection portion. The charge detection portion generates a voltage in dependency upon the transferred charge quantity, and sends it to the amplification portion. The amplification portion amplifies the voltage into an amplified output voltage.
Thereinafter, the above-mentioned operation is repeated at every photo-diodes in the solid-state image device. Thereby, the electric charges from each of the photo-diodes are successively produced in the form of image signals from the amplification portion.
Thus, the image signals can be obtained from the solidstate image device in a time sequence manner. In this event, it is necessary to prevent incidence of the light beam onto the vertical and horizontal CCD registers in order to accurately transfer the electrical charges through the vertical and horizontal CCD registers. To this end, a light shielding film is generally covered over the image region to shield or shade the vertical CCD registers and the horizontal CCD register. In this case, the light shielding film is opened at portions corresponding to the photo-diodes.
Thus, the light shielding film serves to shield both the vertical CCD registers and the horizontal CCD register. Herein, it is to be noted that the light shielding film for the vertical CCD film is formed by the same material as that of the horizontal CCD register. In this event, a metal film is often used as a material of the light shielding film in the conventional solid-state image device.
In consequence, a parasitic capacitor is inevitably caused to occur between the metal film and a charge transfer electrode (namely, an electrode layer) used in each of the horizontal and the vertical CCD registers. This parasitic capacitor leads to an increase of a driving voltage of the horizontal CCD register.
More specifically, it is to be noted that the electrical power in the solid-state image device is mainly consumed by the horizontal CCD register because the horizontal CCD register is driven at a high frequency of 10 MHz while the vertical CCD register is driven at a low frequency of several 10 KHz.
Herein, it is a recent trend that the number of pixels increases with high resolution of the image. In this condition, when a moving picture is projected, the horizontal CCD register must be driven at a higher frequency with the increase of the number of the pixels because a frame frequency is kept at a constant value.
However, as the driving frequency is increased, the power consumption is undesirably increased in the solid-state image device. For example, when the solid-state image device is used for a portable camera and the like, a battery is quickly consumed.
To reduce power consumption in the solid-state image device, it is preferable that the driving voltage of the horizontal CCD register is reduced. This means that the above-mentioned parasitic capacitor of the horizontal CCD register is favorably reduced.
It is therefore an object of this invention to provide a solid-state image device which is capable of reducing a parasitic capacitance with respect to an electrode.
It is another object of this invention to provide a solid-state image device which is capable of driving with high frequency without degradation of image quality.
According to this invention, a solid-state image device includes an image region, a horizontal CCD register, a first light shielding film, and a second light shielding film.
With such a structure, the image region has a plurality of optical-electrical conversion portions (namely, photo-diodes) two-dimensional arranged and a plurality of vertical CCD registers which are placed adjacent to said optical-electrical conversion portions.
In this event, the vertical CCD register vertically transfers electrical charge signals converted by the optical-electrical conversion portions.
The horizontal CCD register is coupled to the vertical CCD registers at one end side, and horizontally transfers the electrical charge signals.
In this condition, a first light shielding film covers the image region except for the optical-electrical conversion portions and is formed by a first material. On the other hand, the second light shielding film covers the horizontal CCD register and is formed by a second material.
Under this circumstance, the first material is different from the second material. Specifically, the first material is metal or metal silicide while the second material is resin.
Moreover, the horizontal CCD register includes a plurality of charge transfer electrodes for transferring the electrical charge signals under the second light shielding film. In this case, the second light shielding film is arranged so as to reduce a parasitic capacitance with respect to the charge transfer electrode.
Namely, a material different from the light shielding film formed for the image region is used as material of the light shielding film formed for the horizontal CCD register according to this invention. As a result, the power consumption of the solidstate image device is largely reduced with high image quality being kept. Further, the solid-state image device can be driven at higher frequency.